[RFC PATCH 1/2] Revert "csky: Fixup CONFIG_DEBUG_RSEQ"

[RFC PATCH 1/2] Revert "csky: Fixup CONFIG_DEBUG_RSEQ"

[Mathieu Desnoyers]

This reverts commit f36e0aab6f1f78d770ce859df3f07a9c5763ce5f.

The csky rseq support has been merged without ever notifying the rseq
maintainers, and without any of the required asssembler glue in the rseq
selftests, which means it is entirely untested.

It is also derived from a non-upstream riscv patch which has known bugs.

The assembly part of this revert should be carefully reviewed by the
architecture maintainer because it touches code which has changed since
the merge of the reverted patch.

The rseq selftests assembly glue should be introduced at the same time
as the architecture rseq support. Without the presence of any test, I
recommend reverting rseq support from csky for now.

Link: https://lore.kernel.org/lkml/1257037909.25426.1626705790861.JavaMail.zimbra@efficios.com/
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Guo Ren <guoren@kernel.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-csky@vger.kernel.org
---
 arch/csky/kernel/entry.S | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/arch/csky/kernel/entry.S b/arch/csky/kernel/entry.S
index 00e3c8ebf9b8..d89afe3b24cc 100644
--- a/arch/csky/kernel/entry.S
+++ b/arch/csky/kernel/entry.S
@@ -50,11 +50,15 @@ ENTRY(csky_systemcall)
 	SAVE_ALL TRAP0_SIZE
 	zero_fp
 	context_tracking
+#ifdef CONFIG_RSEQ_DEBUG
+	mov     a0, sp
+	jbsr    rseq_syscall
+#endif
 	psrset  ee, ie
 
 	lrw     r9, __NR_syscalls
 	cmphs   syscallid, r9		/* Check nr of syscall */
-	bt      1f
+	bt      ret_from_exception
 
 	lrw     r9, sys_call_table
 	ixw     r9, syscallid
@@ -80,11 +84,6 @@ ENTRY(csky_systemcall)
 	jsr     syscallid
 #endif
 	stw     a0, (sp, LSAVE_A0)      /* Save return value */
-1:
-#ifdef CONFIG_DEBUG_RSEQ
-	mov	a0, sp
-	jbsr	rseq_syscall
-#endif
 	jmpi    ret_from_exception
 
 csky_syscall_trace:
@@ -113,10 +112,6 @@ csky_syscall_trace:
 	stw	a0, (sp, LSAVE_A0)	/* Save return value */
 
 1:
-#ifdef CONFIG_DEBUG_RSEQ
-	mov	a0, sp
-	jbsr	rseq_syscall
-#endif
 	mov     a0, sp                  /* right now, sp --> pt_regs */
 	jbsr    syscall_trace_exit
 	br	ret_from_exception
-- 
2.20.1

[RFC PATCH 2/2] Revert "csky: Add support for restartable sequence"

[Mathieu Desnoyers]

This reverts commit 9866d141a0977ace974400bf1f793dfc163409ce.

The csky rseq support has been merged without ever notifying the rseq
maintainers, and without any of the required asssembler glue in the rseq
selftests, which means it is entirely untested.

It is also derived from a non-upstream riscv patch which has known bugs.

The assembly part of this revert should be carefully reviewed by the
architecture maintainer because it touches code which has changed since
the merge of the reverted patch.

The rseq selftests assembly glue should be introduced at the same time
as the architecture rseq support. Without the presence of any test, I
recommend reverting rseq support from csky for now.

Link: https://lore.kernel.org/lkml/1257037909.25426.1626705790861.JavaMail.zimbra@efficios.com/
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Guo Ren <guoren@kernel.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-csky@vger.kernel.org
---
 arch/csky/Kconfig         | 1 -
 arch/csky/kernel/entry.S  | 4 ----
 arch/csky/kernel/signal.c | 3 ---
 3 files changed, 8 deletions(-)

diff --git a/arch/csky/Kconfig b/arch/csky/Kconfig
index 2716f6395ba7..c9655f09e591 100644
--- a/arch/csky/Kconfig
+++ b/arch/csky/Kconfig
@@ -66,7 +66,6 @@ config CSKY
 	select HAVE_PERF_USER_STACK_DUMP
 	select HAVE_DMA_CONTIGUOUS
 	select HAVE_REGS_AND_STACK_ACCESS_API
-	select HAVE_RSEQ
 	select HAVE_STACKPROTECTOR
 	select HAVE_SYSCALL_TRACEPOINTS
 	select MAY_HAVE_SPARSE_IRQ
diff --git a/arch/csky/kernel/entry.S b/arch/csky/kernel/entry.S
index d89afe3b24cc..cc2a7e84c8e5 100644
--- a/arch/csky/kernel/entry.S
+++ b/arch/csky/kernel/entry.S
@@ -50,10 +50,6 @@ ENTRY(csky_systemcall)
 	SAVE_ALL TRAP0_SIZE
 	zero_fp
 	context_tracking
-#ifdef CONFIG_RSEQ_DEBUG
-	mov     a0, sp
-	jbsr    rseq_syscall
-#endif
 	psrset  ee, ie
 
 	lrw     r9, __NR_syscalls
diff --git a/arch/csky/kernel/signal.c b/arch/csky/kernel/signal.c
index 312f046d452d..3cf08732b142 100644
--- a/arch/csky/kernel/signal.c
+++ b/arch/csky/kernel/signal.c
@@ -175,8 +175,6 @@ static void handle_signal(struct ksignal *ksig, struct pt_regs *regs)
 	sigset_t *oldset = sigmask_to_save();
 	int ret;
 
-	rseq_signal_deliver(ksig, regs);
-
 	/* Are we from a system call? */
 	if (in_syscall(regs)) {
 		/* Avoid additional syscall restarting via ret_from_exception */
@@ -262,6 +260,5 @@ asmlinkage void do_notify_resume(struct pt_regs *regs,
 
 	if (thread_info_flags & _TIF_NOTIFY_RESUME) {
 		tracehook_notify_resume(regs);
-		rseq_handle_notify_resume(NULL, regs);
 	}
 }
-- 
2.20.1

Re: [RFC PATCH 2/2] Revert "csky: Add support for restartable sequence"

[Guo Ren]

 Hi Mathieu,

Sorry for forgetting to CC you in the last patch, and that patch has
been merged into master which has the problem of syscall restart.

I still want to keep rseq feature for csky, and implement the
RSEQ_SKIP_FASTPATH for self-test, it that okay?

diff --git a/tools/testing/selftests/rseq/param_test.c
b/tools/testing/selftests/rseq/param_test.c
index 699ad5f93c34..1e67b212ad98 100644
--- a/tools/testing/selftests/rseq/param_test.c
+++ b/tools/testing/selftests/rseq/param_test.c
@@ -208,6 +208,8 @@ unsigned int yield_mod_cnt, nr_abort;
        "bnez " INJECT_ASM_REG ", 222b\n\t" \
        "333:\n\t"

+#elif defined(__csky__)
+#define RSEQ_SKIP_FASTPATH
 #else
 #error unsupported target
 #endif

diff --git a/tools/testing/selftests/rseq/rseq.h
b/tools/testing/selftests/rseq/rseq.h
index 3f63eb362b92..c3dce298b36c 100644
--- a/tools/testing/selftests/rseq/rseq.h
+++ b/tools/testing/selftests/rseq/rseq.h
@@ -79,6 +79,8 @@ extern int __rseq_handled;
 #include <rseq-mips.h>
 #elif defined(__s390__)
 #include <rseq-s390.h>
+#elif defined(__csky__)
+#include <rseq-csky.h>
 #else
 #error unsupported target
 #endif

diff --git a/tools/testing/selftests/rseq/rseq-csky.h
b/tools/testing/selftests/rseq/rseq-csky.h
new file mode 100644
index 000000000000..ecad40e9aeda
--- /dev/null
+++ b/tools/testing/selftests/rseq/rseq-csky.h
@@ -0,0 +1,71 @@
+/* SPDX-License-Identifier: LGPL-2.1 OR MIT */
+
+#if __ORDER_LITTLE_ENDIAN__ == 1234
+#define RSEQ_SIG       0xc1e6643f  /* mtcr    r6, cr<31, 15> */
+#else
+#error "Currently, RSEQ only supports Little-Endian version"
+#endif
+
+/*
+ * bar.brwarws: ordering barrier for all load/store instructions
+ *              before/after
+ *
+ * |31|30 26|25 21|20 16|15  10|9   5|4           0|
+ *  1  10000 00000 00000 100001        00001 0 bw br aw ar
+ *
+ * b: before
+ * a: after
+ * r: read
+ * w: write
+ *
+ * Here are all combinations:
+ *
+ * bar.brw
+ * bar.br
+ * bar.bw
+ * bar.arw
+ * bar.ar
+ * bar.aw
+ * bar.brwarw
+ * bar.brarw
+ * bar.bwarw
+ * bar.brwar
+ * bar.brwaw
+ * bar.brar
+ * bar.bwaw
+ */
+#define __bar_brw()    asm volatile (".long 0x842cc000\n":::"memory")
+#define __bar_br()     asm volatile (".long 0x8424c000\n":::"memory")
+#define __bar_bw()     asm volatile (".long 0x8428c000\n":::"memory")
+#define __bar_arw()    asm volatile (".long 0x8423c000\n":::"memory")
+#define __bar_ar()     asm volatile (".long 0x8421c000\n":::"memory")
+#define __bar_aw()     asm volatile (".long 0x8422c000\n":::"memory")
+#define __bar_brwarw() asm volatile (".long 0x842fc000\n":::"memory")
+#define __bar_brarw()  asm volatile (".long 0x8427c000\n":::"memory")
+#define __bar_bwarw()  asm volatile (".long 0x842bc000\n":::"memory")
+#define __bar_brwar()  asm volatile (".long 0x842dc000\n":::"memory")
+#define __bar_brwaw()  asm volatile (".long 0x842ec000\n":::"memory")
+#define __bar_brar()   asm volatile (".long 0x8425c000\n":::"memory")
+#define __bar_brar()   asm volatile (".long 0x8425c000\n":::"memory")
+#define __bar_bwaw()   asm volatile (".long 0x842ac000\n":::"memory")
+
+#define rseq_smp_mb()  __bar_brwarw()
+#define rseq_smp_rmb() __bar_brar()
+#define rseq_smp_wmb() __bar_bwaw()
+
+#define rseq_smp_load_acquire(p)                                       \
+__extension__ ({                                                       \
+       __typeof(*p) ____p1 = RSEQ_READ_ONCE(*p);                       \
+       __bar_brarw();                                                  \
+       ____p1;                                                         \
+})
+
+#define rseq_smp_acquire__after_ctrl_dep()     rseq_smp_rmb()
+
+#define rseq_smp_store_release(p, v)                                   \
+do {                                                                   \
+       __bar_brwaw();                                                  \
+       RSEQ_WRITE_ONCE(*p, v);                                         \
+} while (0)
+
+#include "rseq-skip.h"

On Sat, Jul 24, 2021 at 12:16 AM Mathieu Desnoyers
<mathieu.desnoyers@efficios.com> wrote:
>
> This reverts commit 9866d141a0977ace974400bf1f793dfc163409ce.
>
> The csky rseq support has been merged without ever notifying the rseq
> maintainers, and without any of the required asssembler glue in the rseq
> selftests, which means it is entirely untested.
>
> It is also derived from a non-upstream riscv patch which has known bugs.
I noticed that in [1]:

As Al Viro pointed out on IRC, the rseq_signal_deliver() should go after syscall
restart handling, similarly to what is done on every other supported
architecture.

[1] https://lore.kernel.org/linux-riscv/1257037909.25426.1626705790861.JavaMail.zimbra@efficios.com/

I still want to fixup it, instead of revert it.

>
> The assembly part of this revert should be carefully reviewed by the
> architecture maintainer because it touches code which has changed since
> the merge of the reverted patch.
>
> The rseq selftests assembly glue should be introduced at the same time
> as the architecture rseq support. Without the presence of any test, I
> recommend reverting rseq support from csky for now.
>
> Link: https://lore.kernel.org/lkml/1257037909.25426.1626705790861.JavaMail.zimbra@efficios.com/
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> Cc: Guo Ren <guoren@kernel.org>
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: linux-csky@vger.kernel.org
> ---
>  arch/csky/Kconfig         | 1 -
>  arch/csky/kernel/entry.S  | 4 ----
>  arch/csky/kernel/signal.c | 3 ---
>  3 files changed, 8 deletions(-)
>
> diff --git a/arch/csky/Kconfig b/arch/csky/Kconfig
> index 2716f6395ba7..c9655f09e591 100644
> --- a/arch/csky/Kconfig
> +++ b/arch/csky/Kconfig
> @@ -66,7 +66,6 @@ config CSKY
>         select HAVE_PERF_USER_STACK_DUMP
>         select HAVE_DMA_CONTIGUOUS
>         select HAVE_REGS_AND_STACK_ACCESS_API
> -       select HAVE_RSEQ
>         select HAVE_STACKPROTECTOR
>         select HAVE_SYSCALL_TRACEPOINTS
>         select MAY_HAVE_SPARSE_IRQ
> diff --git a/arch/csky/kernel/entry.S b/arch/csky/kernel/entry.S
> index d89afe3b24cc..cc2a7e84c8e5 100644
> --- a/arch/csky/kernel/entry.S
> +++ b/arch/csky/kernel/entry.S
> @@ -50,10 +50,6 @@ ENTRY(csky_systemcall)
>         SAVE_ALL TRAP0_SIZE
>         zero_fp
>         context_tracking
> -#ifdef CONFIG_RSEQ_DEBUG
> -       mov     a0, sp
> -       jbsr    rseq_syscall
> -#endif
>         psrset  ee, ie
>
>         lrw     r9, __NR_syscalls
> diff --git a/arch/csky/kernel/signal.c b/arch/csky/kernel/signal.c
> index 312f046d452d..3cf08732b142 100644
> --- a/arch/csky/kernel/signal.c
> +++ b/arch/csky/kernel/signal.c
> @@ -175,8 +175,6 @@ static void handle_signal(struct ksignal *ksig, struct pt_regs *regs)
>         sigset_t *oldset = sigmask_to_save();
>         int ret;
>
> -       rseq_signal_deliver(ksig, regs);
> -
>         /* Are we from a system call? */
>         if (in_syscall(regs)) {
>                 /* Avoid additional syscall restarting via ret_from_exception */
> @@ -262,6 +260,5 @@ asmlinkage void do_notify_resume(struct pt_regs *regs,
>
>         if (thread_info_flags & _TIF_NOTIFY_RESUME) {
>                 tracehook_notify_resume(regs);
> -               rseq_handle_notify_resume(NULL, regs);
>         }
>  }
> --
> 2.20.1
>


--
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/

Re: [RFC PATCH 2/2] Revert "csky: Add support for restartable sequence"

[Mathieu Desnoyers]

----- On Jul 26, 2021, at 12:10 PM, Guo Ren guoren@kernel.org wrote:

> Hi Mathieu,
> 
> Sorry for forgetting to CC you in the last patch, and that patch has
> been merged into master which has the problem of syscall restart.
> 
> I still want to keep rseq feature for csky, and implement the
> RSEQ_SKIP_FASTPATH for self-test, it that okay?

No, the RSEQ_SKIP_FASTPATH is the one special-case of test build which
skips building rseq critical sections entirely. This leaves out any
relevant testing of rseq per-se. With what we have in the upstream
selftests, I expect this test configuration to abort at runtime because
no slow-path fallbacks are available when the fastpath is disabled.

The asm glue to test rseq user-space really needs to be implemented
for any useful testing to be done here.

Unless that asm glue is contributed, none of the rseq logic is actually
tested on that architecture.

Considering the extremely-hard-to-debug nature of races with a broken
rseq kernel implementation, proper testing coverage is paramount, so I
still recommend the revert unless the selftests user-space asm glue is
contributed for C-Sky.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com

Re: [RFC PATCH 2/2] Revert "csky: Add support for restartable sequence"

[Mathieu Desnoyers]

On 2021-07-26 12:28, Mathieu Desnoyers wrote:
> ----- On Jul 26, 2021, at 12:10 PM, Guo Ren guoren@kernel.org wrote:
> 
>> Hi Mathieu,
>>
>> Sorry for forgetting to CC you in the last patch, and that patch has
>> been merged into master which has the problem of syscall restart.
>>
>> I still want to keep rseq feature for csky, and implement the
>> RSEQ_SKIP_FASTPATH for self-test, it that okay?
> 
> No, the RSEQ_SKIP_FASTPATH is the one special-case of test build which
> skips building rseq critical sections entirely. This leaves out any
> relevant testing of rseq per-se. With what we have in the upstream
> selftests, I expect this test configuration to abort at runtime because
> no slow-path fallbacks are available when the fastpath is disabled.
> 
> The asm glue to test rseq user-space really needs to be implemented
> for any useful testing to be done here.
> 
> Unless that asm glue is contributed, none of the rseq logic is actually
> tested on that architecture.
> 
> Considering the extremely-hard-to-debug nature of races with a broken
> rseq kernel implementation, proper testing coverage is paramount, so I
> still recommend the revert unless the selftests user-space asm glue is
> contributed for C-Sky.

Hi Guo,

A friendly ping after 1.5 year about the fact that the selftests code is
still missing for the csky architecture. So there is no way to validate
that the kernel pieces that were merged actually work on that architecture.

What is the timeline for contribution of the missing bits needed to enable
those tests ?

Here are the required header files:

tools/testing/selftests/rseq/rseq-csky.h
tools/testing/selftests/rseq/rseq-csky-thread-pointer.h (only if __builtin_thread_pointer is not implemented by gcc)

I'm open to suggestions from other rseq co-maintainers on how to best address
this situation.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com

Re: [RFC PATCH 2/2] Revert "csky: Add support for restartable sequence"

[Guo Ren]

On Sat, Sep 10, 2022 at 4:01 AM Mathieu Desnoyers
<mathieu.desnoyers@efficios.com> wrote:
>
> On 2021-07-26 12:28, Mathieu Desnoyers wrote:
> > ----- On Jul 26, 2021, at 12:10 PM, Guo Ren guoren@kernel.org wrote:
> >
> >> Hi Mathieu,
> >>
> >> Sorry for forgetting to CC you in the last patch, and that patch has
> >> been merged into master which has the problem of syscall restart.
> >>
> >> I still want to keep rseq feature for csky, and implement the
> >> RSEQ_SKIP_FASTPATH for self-test, it that okay?
> >
> > No, the RSEQ_SKIP_FASTPATH is the one special-case of test build which
> > skips building rseq critical sections entirely. This leaves out any
> > relevant testing of rseq per-se. With what we have in the upstream
> > selftests, I expect this test configuration to abort at runtime because
> > no slow-path fallbacks are available when the fastpath is disabled.
> >
> > The asm glue to test rseq user-space really needs to be implemented
> > for any useful testing to be done here.
> >
> > Unless that asm glue is contributed, none of the rseq logic is actually
> > tested on that architecture.
> >
> > Considering the extremely-hard-to-debug nature of races with a broken
> > rseq kernel implementation, proper testing coverage is paramount, so I
> > still recommend the revert unless the selftests user-space asm glue is
> > contributed for C-Sky.
>
> Hi Guo,
>
> A friendly ping after 1.5 year about the fact that the selftests code is
> still missing for the csky architecture. So there is no way to validate
> that the kernel pieces that were merged actually work on that architecture.
>
> What is the timeline for contribution of the missing bits needed to enable
> those tests ?
I would send the 1st version of patchset before 2022/10/30, or just
revert it from csky.

1. a patch for fixup the bug:
diff --git a/arch/csky/kernel/signal.c b/arch/csky/kernel/signal.c
index b7b3685283d7..434dcf2e8e37 100644
--- a/arch/csky/kernel/signal.c
+++ b/arch/csky/kernel/signal.c
@@ -179,8 +179,6 @@ static void handle_signal(struct ksignal *ksig,
struct pt_regs *regs)
        sigset_t *oldset = sigmask_to_save();
        int ret;

-       rseq_signal_deliver(ksig, regs);
-
        /* Are we from a system call? */
        if (in_syscall(regs)) {
                /* Avoid additional syscall restarting via ret_from_exception */
@@ -206,6 +204,8 @@ static void handle_signal(struct ksignal *ksig,
struct pt_regs *regs)
                }
        }

+       rseq_signal_deliver(ksig, regs);
+
        /* Set up the stack frame */
        ret = setup_rt_frame(ksig, oldset, regs);

2. Add tools/testing/selftests/rseq/rseq-csky* codes.



>
> Here are the required header files:
>
> tools/testing/selftests/rseq/rseq-csky.h
> tools/testing/selftests/rseq/rseq-csky-thread-pointer.h (only if __builtin_thread_pointer is not implemented by gcc)
>
> I'm open to suggestions from other rseq co-maintainers on how to best address
> this situation.
>
> Thanks,
>
> Mathieu
>
> --
> Mathieu Desnoyers
> EfficiOS Inc.
> https://www.efficios.com



-- 
Best Regards
 Guo Ren

Re: [RFC PATCH 2/2] Revert "csky: Add support for restartable sequence"

[Mathieu Desnoyers]

On 2022-09-09 22:35, Guo Ren wrote:
> On Sat, Sep 10, 2022 at 4:01 AM Mathieu Desnoyers
[
>> A friendly ping after 1.5 year about the fact that the selftests code is
>> still missing for the csky architecture. So there is no way to validate
>> that the kernel pieces that were merged actually work on that architecture.
>>
>> What is the timeline for contribution of the missing bits needed to enable
>> those tests ?
> I would send the 1st version of patchset before 2022/10/30, or just
> revert it from csky.

OK. I can help by answering questions or with code review. I'm not 
fluent in csky assembly, but I'll try to learn as I go.

> 
> 1. a patch for fixup the bug:
> diff --git a/arch/csky/kernel/signal.c b/arch/csky/kernel/signal.c
> index b7b3685283d7..434dcf2e8e37 100644
> --- a/arch/csky/kernel/signal.c
> +++ b/arch/csky/kernel/signal.c
> @@ -179,8 +179,6 @@ static void handle_signal(struct ksignal *ksig,
> struct pt_regs *regs)
>          sigset_t *oldset = sigmask_to_save();
>          int ret;
> 
> -       rseq_signal_deliver(ksig, regs);
> -
>          /* Are we from a system call? */
>          if (in_syscall(regs)) {
>                  /* Avoid additional syscall restarting via ret_from_exception */
> @@ -206,6 +204,8 @@ static void handle_signal(struct ksignal *ksig,
> struct pt_regs *regs)
>                  }
>          }
> 
> +       rseq_signal_deliver(ksig, regs);
> +
>          /* Set up the stack frame */
>          ret = setup_rt_frame(ksig, oldset, regs);

Yes, this fix is really needed.

> 
> 2. Add tools/testing/selftests/rseq/rseq-csky* codes.

It looks like a good plan,

Thanks,

Mathieu


> 
> 
> 
>>
>> Here are the required header files:
>>
>> tools/testing/selftests/rseq/rseq-csky.h
>> tools/testing/selftests/rseq/rseq-csky-thread-pointer.h (only if __builtin_thread_pointer is not implemented by gcc)
>>
>> I'm open to suggestions from other rseq co-maintainers on how to best address
>> this situation.
>>
>> Thanks,
>>
>> Mathieu
>>
>> --
>> Mathieu Desnoyers
>> EfficiOS Inc.
>> https://www.efficios.com
> 
> 
> 


-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com